Generally, in an airplane, screens are integrated in each seat as much for the broadcasting of entertainment programs (music, films, video games, etc.) as for the transmission of safety messages (buckling of belts, use of electronic devices, etc.). These screens are connected within a network to a central computer or server.
Thus, FIG. 1 shows a prior-art network 1, in which screens 2.1-2.N of seats 3.1-3.N are connected to a server 4. These screens 2.1-2.N are connected to the server 4 via network switches 4.1-4.3 or switches. These switches 4.1-4.3 transmit the information received on one of their ports to the screen to which it is intended. The cables 5, which ensure the links between the switches 4.1-4.3 and the server 3, are copper cables in which signals circulate that are generally the standard of the Ethernet bus.
This type of network has the drawback of being heavy since copper is a high-density metal. One solution consists of replacing it with aluminum, whose density is 3.3 times lighter. However, since aluminum is not used very widely—at least for cables of small sections, it poses difficulties in terms of connecting to connectors, as well as in terms of contact quality and risk of corrosion.
In addition, this type of network produces a relatively intense electromagnetic field, which makes it necessary to take a lot of precautions as much for preventing interference with electronic equipment in the vicinity as for being parasitized by the equipment of the airplane.
Moreover, as the network switches 4.1-4.3 do need a power supply, the risks of failure can never be entirely eliminated. Now, if one of the switches 4.1-4.3 fails, all the screens 2.1-2.N of the seats located downstream are inoperative. Not only are passengers deprived of their entertainment programs, but, more importantly, the safety instructions can no longer be displayed on a significant number of seats.
The above-mentioned drawbacks disappear if the copper cable 5 is replaced with an optical fiber cable 9 because it becomes possible to use, perpendicular to each seat, entirely passive optical couplers 10.1-10.3, as shown in FIG. 2.
These optical couplers 10.1-10.3 replace the previous switches. These optical couplers 10.1-10.3 are light shunters which do not comprise any component capable of failing and do not require any electric power supply. The weight of the fiber by itself is negligible, and the light beam not only does not generate parasitics, but is not susceptible to interfering electromagnetic fields.
Such a network is called a PON network (for Passive Optical Network in English). In this network, the transceivers 11.1-11.3 and 12 (transceiver in English) are positioned between the communicating elements (screens or server) and the couplers for converting the electric signals into light signals and vice versa.
However, each coupler 10.1-10.3 introduces an attenuation of the signal which limits the number of seats connected to a single fiber. In fact, a passive optical network can hardly serve more than 12 seats, which makes it necessary either to multiply the number of optical fibers or to re-amplify the light signal every 12 couplers, in which case, we again find the risks of failures of the Ethernet bus affecting copper cables.